1. Field of the Invention
The present invention relates to an AC surface discharging plasma display panel, and more particularly, to a surface discharging plasma display panel according to an electrode wiring structure and a method for driving the plasma display panel for displaying gray scales.
2. Description of Related Art
A plasma display panel is of a display device for displaying picture data input as an electrical signal by arranging a plurality of discharge tubes in a matrix and by selectively emitting light from them. Methods for driving the plasma display panel are divided into DC driving methods and AC driving methods according to whether the polarity of a pulse voltage applied in order to sustain the discharge changes over time.
FIG. 1A is a sectional view of a DC opposite surface discharge plasma display panel. FIGS. 2A and 2B are respectively a sectional view and perspective view of an AC surface discharge plasma display panel. As shown in the drawings, in both DC and AC types, a discharge space is formed between upper glass plates 1 or 7 and lower glass plates 4 or 12. In the DC plasma display panel, the flow of electrons is from a negative pole becomes a main energy source for sustaining the discharge, since a scanning electrode 2 and an address electrode 5 are directly exposed to a discharge space 3. In the AC plasma display panel, a scanning electrode 6a and a common electrode 6b for sustaining the discharge are electrically separated from a discharge space 10 by a dielectric layer 8. In the case of the AC plasma display panel, the discharge is sustained by a well known wall charge effect. Namely, the discharge occurs only in a place where the wall charge exists, since a discharge resuming voltage is the sum of a wall voltage and an applied voltage. The discharge is continuously sustained in the place where the discharge first occurred, since the discharge replenishes the wall charge.
Electrode structures are divided into opposite surface discharge structures and surface discharge structures. Namely, the opposite surface discharge electrodes have a structure in which electrodes for generating the discharge are on opposite surfaces of the discharge space. On the other hand, the surface discharge electrodes have a structure in which the electrodes for generating the discharge are both arranged in the same plane, as shown in FIG. 2A. Electrode structures are also divided into two electrode structures and three electrode structures, according to the number of electrodes installed for realizing a discharge.
FIG. 2B shows the three electrode surface discharge structure of the plasma display panel in common use. An address electrode 11 is opposite and perpendicular to the two parallel display electrodes, i.e., the scanning electrode 6a and the common electrode 6b. The discharge spaces are defined by latticed walls. In the structure, the discharge for generating the wall charge is generated in order to select pixels between the address electrode 11 and the scanning electrode 6a. Then, the discharge for displaying pictures is maintained for a certain time between the scanning electrode 6a and the common electrode 6b. A latticed wall 17 defines the discharge spaces and prevents cross talk between adjacent pixels by intercepting light generated by the discharge. The pixels are constructed by forming a plurality of unit structures on a substrate in a matrix and applying a fluorescent material to the unit structures. Such pixels form a plasma display panel. In the plasma display panel in common use, when the discharge is generated in a pixel, ultra-violet rays generated by the discharge excite the fluorescent material coating on the inner wall of the pixel, thus realizing a desired color.
Displaying gray scales is a prerequisite for displaying colors on the plasma display panel. A method of dividing a 1TV field into a plurality of auxiliary fields and time division controlling them is used for realizing gray scales. FIG. 3 describes the gray scale display method of the AC plasma display panel. This is a 6 bit gray scale display method, in which a TV fields is divided into 6 auxiliary fileds (SF1, SF2, . . . , SF6) and each auxiliary field is divided into address periods (A1, A2, . . . , A6) and discharge sustaining periods (S1, S2, S3, . . . , S6). Here, the pixels of the display panel are selected during the address periods (A1, A2, . . . , A6). The gray scales of the pixels selected during the address periods are displayed by the combination of the discharge sustaining periods (S1, S2, S3, . . . , S6). 64 gray scales may be displayed by this method. Namely, 64 gray scale levels 0 to 63 are selected from the plasma display panel having 480 scanning lines (Y1, Y2, . . . , Y480). For example, the gray scales are displayed as follows; 0(0T), 1(1T), 2(2T), 3(1T+2T), 4(4T), 5(1T+4T), 6(2T+4T), 7(1T+2T+4T), 8(8T), 9(1T+8T), . . . , 27(1T+2T+8T+16T), . . . , 63(1T+2T+4T+8T+16T+32T).
FIG. 4 shows an example of the electrode wiring structure of the AC plasma display panel in common use. In the structure, there are two sets of parallel electrodes (X and Y electrodes), horizontally facing each other in pairs, and address electrodes 21, perpendicular to the X and Y electrodes. Here, the X electrodes are common electrodes and are connected in common. The Y electrodes are scanning electrodes. The waveforms of a drive signal for driving the AC plasma display panel having the present wiring structure are shown in FIG. 5. The address discharge and the sustaining discharge are separately driven by the drive signal. In FIG. 5, the waveforms of an address discharge drive signal (A), scanning electrode drive signals (Y1, Y2, . . . , Y480), and a common electrode drive signal(X) are shown. Here, only the signal of a first sub-field (SF1) is shown. A1 and S1 respectively denote a first address period and a first discharge sustaining period. The address period (A1; the first address period) is constructed by the erasing period having a complete erasing period (A11), a complete writing period (A12), a complete erasing period (A13), and an actual address period (A14). During the erasing period (A11, A12, and A13), the wall charges generated by a previous discharge are erased in all cells by generating a weak discharge (A11), new wall charges are written (A12) in all cells, and the new wall charges are partially erased in all cells (A13) so that only appropriate wall charges remain in order to correctly display gray scales. Accordingly, the next auxiliary field (SH2) operates smoothly. During the address period (A14), the wall charge is formed by the scanning electrode in a place on the screen of the plasma display panel selected by a selective discharge by a write pulse between the address electrode and the scanning electrode, and information is written by electric signal. During the discharge sustaining period (S1), image information is realized as gray scales by the discharge generated by continuous discharge sustaining pulses. In the discharge sustaining period(S1), light is continuously emitted.
However, in the gray scale method of the plasma display panel, the discharge sustaining period (S1) is assigned on the basis of an NTSC level of a 6 bit gray scale and amounts to less than 30% of a one frame image display period since the address discharge is driven separately from the sustaining discharge. Therefore, the brightness of the plasma display panel is very low, which is a serious drawback. In the case of being applied to a high definition display device, the discharge sustaining period is further reduced to 1/2 of the present level, thus the brightness is even more severely lowered. Also, when a larger number of gray scales are made available, the discharge sustaining period is again reduced, thus also reducing the brightness. In order to improve the brightness, more pulse rows may be applied in 1 sub-field by increasing the frequency and narrowing the width of the discharge sustaining pulse. In the case of increasing the frequency of the discharge sustaining pulse, the space charge caused by the discharge generated by one pulse affects the discharge characteristic of the next discharge, since the rows of discharge sustaining pulses periodically coincide, and thus the discharge becomes unstable. Accordingly, the increase of the brightness reaches saturation. In the case of narrowing the width of the discharge sustaining pulse, the discharge sustaining voltage increases since less time is available for converting the space charge generated after the discharge into the wall charge.
To solve such problems, a method such as the one shown in FIG. 6 is used. This method simultaneously drives the addressing discharge and the sustaining discharge, instead of separately driving the addressing discharge and the sustaining discharge. In the method, address pulses 29a, 29b, and 29c are applied in the periods between the discharge sustaining pulses 32 applied to the respective scanning electrodes Y1, Y2, and Y3. Erasing pulses 31a and 31b for performing the igniting and scanning pulses 33a, 33b, and 33c for performing the addressing discharge are applied to the periods between the discharge sustaining pulses 32 applied to the scanning electrodes Y1, Y2, and Y3. Then, the length of the discharge sustaining period is set. A method of using the entire 1TV frame for sustaining the discharge by dividing the 1TV frame into auxiliary frames (SF1 through SF8) as shown in FIG. 7 is used for displaying the gray scales. However, there are many restrictions in determining the timing for inserting the address pulses since the address pulses must be inserted between the discharge sustaining pulses. Therefore, the number of displayable scanning lines is limited, and it is difficult to drive the addressing discharge and sustaining discharge of a high definition display. In order to solve these problems, the discharges must be driven at a high speed, such as two or three times normal speed. In this case, the discharge becomes unstable due to the increase of the frequency and the discharge sustaining voltage increases due to the reduction of the width of the discharge sustaining pulse, as mentioned above.